Not Applicable
1. Field of the Invention
This invention relates to medical device delivery catheters in general, and specifically to balloon catheters for use in delivering a medical device such as a stent to a desired body location, such as in a blood vessel. More specifically, this invention relates to socks or sleeves used in retaining the stent in the unexpanded state which have reduced frictional engagement with the ends of a stent and/or balloon cones. In the present invention such reduced frictional interaction is made possible by providing the sleeve or sleeves with an inside surface of which at least a portion is characterized as being harder than the outside surface.
2. Description of the Related Art
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under positive external pressure in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents may be crimped to their reduced diameter about the delivery catheter, maneuvered to the deployment site, and expanded to the vessel diameter by fluid inflation of a balloon positioned on the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al, relates to an expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. That patent discloses a stent delivery system in which a catheter carries, on its distal end portion, a stent which is held in place around the catheter prior to and during percutaneous delivery by means of one and preferably two sleeves. The sleeves are positioned around the catheter with one end portion attached thereto and overlap an end portion(s) of the stent to hold it in place on the catheter in a contracted condition. Each sleeve is elastomeric in nature so as to stretch and release the stent when it expands for implantation. The stent is expandable by means of the expandable balloon on the catheter. During expansion of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site.
Copending U.S. patent application Ser. No. 09/407,836 which was filed on Sep. 28, 1999 and entitled Stent Securement Sleeves and Optional Coatings and Methods of Use, and which is incorporated in its entirety herein by reference, also provides for a stent delivery system having sleeves. In 09/407,836 the sleeves may be made up of a combination of polytetrafluoroethylene (PTFE) as well as one or more thermoplastic elastomers. Other references exist which disclose a variety of stent retaining sleeves.
A common problem which occurs in catheter assemblies is friction or adhesion between various parts which periodically come into contact with one another during the medical procedure. For instance, friction can occur between the guide catheter and guide wire, between the introducer sheath and the guide catheter, or between the guide catheter and the balloon catheter, for instance, and may increase the difficulty of insertion, cause loss of catheter placement, and result in discomfort to the patient or damage to the vasculature. In catheters equipped with stent retaining socks or sleeves, friction between the balloon and sleeve, and/or the stent and sleeve may also cause retraction of the sleeves to be made more difficult. In stent delivery systems where the stent employs a relatively soft coating material on it surface, such as a drug carrier, the relatively soft coating may increase its friction to the sock or sleeve system. An example of which may be seen in U.S. Pat. No. 5,693,085 to Buirge et al., the entire contents of which is incorporated herein by reference.
It is therefore desirable to reduce the friction due to the sliding between the various parts of the catheter assemblies. Copending U.S. application Ser. No. 09/549,286 which was filed Apr. 14, 2000 describes a reduced columnar strength stent retaining sleeve having a plurality of holes. The relatively reduced columnar and radial strength provided by the holes allows the sleeve to be retracted off of a stent without the need for lubricant.
Lubricants however may be used in a variety of stent delivery catheters. Many lubricants and lubricious coatings types have been used in conjunction with balloon catheters. Both hydrophilic and hydrophobic coatings and lubricants are well known in the catheter art. For example: copending U.S. patent application Ser. No. 09/407,836 which was filed on Sep. 28, 1999 and entitled Stent Securement Sleeves and Optional Coatings and Methods of Use, provides for a stent delivery system having sleeves. In Ser. No. 09/407,836 the sleeves may be made up of a combination of polytetrafluoroethylene (hereinafter PTFE) as well as one or more thermoplastic elastomers. Copending U.S. patent application Ser. No. 09/427,805 filed Oct. 27, 1999, and entitled End Sleeve Coating for Stent Delivery, describes the use of stent retaining sleeves having lubricious coatings applied thereto.
Copending U.S. patent application Ser. No. 09/273,520 filed Mar. 22, 1999, entitled Lubricated Sleeve Material For Stent Delivery likewise describes the use of stent retaining sleeves and lubricants.
Stent delivery systems which may not require the use of lubricants have been proposed, such as copending U.S. application Ser. No. 09/549,286 mentioned above. Another example of a stent delivery system and retaining sleeve which may not require lubrication is Copending application Ser. No. 09/668,496 filed Sep. 22, 2000 and entitled Striped Sleeve For Stent Delivery describes a two component sleeve having one or more substantially longitudinally oriented stripe of a hard material and a softer material. The striped configuration of materials in the sleeve allows the sleeve to radially expand but with limited or no longitudinal expansion. The unique expansion characteristics provided by the striped configuration helps avoid a need to use a lubricant with the sleeve, though a lubricant may still be utilized therewith if desired.
The entire content of all patents and applications listed within the present patent application are incorporated herein by reference.
The instant invention is directed to a medical device delivery system comprising a catheter assembly having a medical device receiving region and at least one retaining sleeve for retaining the medical device on the receiving region prior to delivery. An expandable medical device, such as a stent, is disposed about the medical device receiving region of the catheter assembly. At least one retaining sleeve is disposed about an end of the expandable medical device and at least a portion of the catheter assembly.
The at least one retaining sleeve further comprises an inside surface and an outside surface. The outside surface being comprised of a first material and at least the portion of the inside surface which is constructed to overlay a stent being comprised of a second material. The first and second materials having different harnesses, the second material being harder than the first. As is known, for most polymer materials, the hardness represents the capacity of elongation when the polymer is exposed to an outside acting force, this is especially true for elastomeric materials (e.g. the lower a material""s hardness the higher the material""s elasticity).
Unlike the Ser. No. 09/668,496 application, from which the present application depends, and which provides for a sleeve having reduced longitudinal elongation, the present invention improves sleeve retractability by providing at least the portion of the inside surface of the sleeve which may overlay a stent with a material which has a greater hardness than the majority of the sleeve material. Such a relatively hard material preferably provides the sleeve with a surface having lower frictional engagement to the stent.
In an embodiment of the invention the first material and second material are co-extruded polymers.
In an embodiment of the invention the second material is a coating on the first material.
In an embodiment of the invention the inside surface is comprised entirely of the second material.
In an embodiment of the invention only the portion of the inside surface which is constructed and arranged to overlay a stent is comprised of the harder material.